Reversing heat exchanger unit

ABSTRACT

A reversing heat exchanger system not divided into the usual blocks and having change-over valves and check valves provided in each reversing heat exchanger unit to unify them and thereby to prevent the loss of raw air upon exchange of raw air and waste gas paths, to prevent abrupt pressure changes, to enable stable operation of a rectification system, and to standardize the change-over valves and check valves in order to facilitate easy design and manufacturing of the reversing heat exchanger system.

United States Patent 1 1 Nakanishi Nov. 6, 1973 [54] REVERSING HEATEXCHANGER UNIT 2,737,970 3/l956 I Hasche et al. l37/309 5] Inventor:3,25l,l90 5/1966 Seldel 62/l4 [73] Assignee: Kobe Steel, Ltd.,Fukiai-ku, Kobe, FOREIGN PATENTS F APPLICATIONS Japan 899,334 6/1962Great Brltaln 62/13 Filed; y 15, 1971 Primary ExaminerAlbert W. Davis,Jr. 21 p NOJ 1 2 35 Att0rney-N0rman F. Oblon el al.

[52] US. Cl 165/97, 62/l3, 62/15, [57] ABSTRACT 137/309 137/512 137/595A reverslng heat exchanger system not d1v1ded mm the 51 1m. 01 F28f27/02 usual blocks and having change/Over valves and Check [58] Field ofSearch 165/97' 137/309 Valves Pm"ided each reversing heat exchanger137/512 595; 62/13 14, 15; 210/277 278 to unify them and thereby toprevent the loss of raw air upon exchange of raw air and waste gaspaths, to pre- [56] References Cited vent abrupt pressure changes, toenable stable opera- UNITED STATES PATENTS tion of a rectificationsystem, and to standardize the changeover valves and check valves inorder to faciliy et tate easy design and manufacturing of the reversingervm v 2,107,335 2/1938 Linde et al 62/13 x heat exchanger System 5Claims, 10 Drawing Figures PATENTEDMUVI 6197s 3770.050 SHEET 1 CF 5 vINVENTOR SADAYUKI NAKANISHI BY (Q M,

ATTORNEYS PATENTEDNnv 6 I973 SHUT 5 CF 5 L% wm" NvELMv REVERSING HEATEXCHANGER UNIT BACKGROUNDOF THE INVENTION This invention relatesgenerally to reversing heat exchanger units used in low temperature airseparators and more particularly to a unified reversing heat exchangercharacterized by the provision of a novel arrangement of change-overvalves and check valves in a conventional reversing heat exchanger.

Heretofore, standardization of conventional air separators has been verydifficult because the separators usually have several blocks of heatexchangers, each block in turn having change-over valves and checkvalves, and yet the number of blocks and the number of heat exchangersin any one block are optionally determined by the capacity of theseparator, whereby the size and number of the change-over valves andcheck valves depend variably upon the design conditions thereof so thatnot only the capacity of the change-over valves and the check valves,but the related components, such as piping, cold box, and the like mustbe designed into every separator. Since the capacity of a single heatexchanger is substantially constant for the convenience ofmanufacturing, the number of the reversing heat exchanger units isdetermined by the desired capacity of the air separator, but since thenumber of heat exchangers in one block and the number of blocks arecontrary to each other, it is necessary to enlarge the capacity of thecheck valves and the diameter of the ports of the change-over valves,when the number of heat exchangers in one block is increased so that'thetreating capacity of the block becomes larger, in order to decrease thetotal number of the change-over valves and check valves. In order todecrease the diameter of the port of the change-over valves and thecapacity of the check valves, it is necessary to increase the number ofthe blocks and to increase the total number of the change-over valvesand-check valves. Accordingly, as the sizes of the change-over valvesand check valves are different depending upon various design conditions,it is difficult to unify the change-over. valves and check valves forsuch heat exchanger systems. l

The exchange of raw air and waste gasfrom their respective paths isconducted by a plurality of changeover valves provided in every block ofheat exchangers such as, for example, in the case of a block consistingof six reversing heat exchanger units shown in FIG. 1 illustrating aconventional reversing heat exchanger system in an air separator, insuch a manner that raw air compressed to approximately 5 atm. is fedfrom a pipe 1 through an open change-over valve C pipe 2, main pipe 12,and respective flow rate control valves D, to heat exchangers A, throughA,, to be distributed thereto for being cooled to approximately -l70 C.upon heat exchange with a waste gas and other product gases, whereuponit is gathered into a main pipe 10 for passage through a pipe 3, a checkvalve B and a pipe 4 leading to the next rectification process. On theother hand, waste gas of approximately 0.2 atm. being fed from therectification system is distributed through pipes 5 and 6, check valve3,, pipe 7 and main pipe 11 into the waste gas path of the heatexchangers and is gathered therefrom into a main pipe 13 throughrespective flow rate control valves D associated with the units A, -A,,at a normal temperature, and is then fed out of the separator through apipe 8, and an open change-over valve C Raw air of the reversing heatexchanger andwaste gas, such as, for example, waste nitrogen, paths areexchanged by an exchanging operation of the change-over valves C throughC,. For example, if the valves C and C are open and the valves C,, C andC are closed, as just described, they are exchanged by closing thevalves C and C.,, thereby momentarily completely shutting off the rawair and gas flow paths, then opening the valve C to equalize thepressure of the raw'air and waste gas paths at approximately 2.6 atm.,then closing the valve C and finally opening the valves C and C in orderto complete the exchange of the paths. In FIG. 1, the paths of productgases not concerned with the exchange are omitted.

Because such systems require not only complicated switching operations,but main pipes 10, ll, 12 and 13 for gathering the raw air and waste gasbeing fed into and from the respective heat exchangers, when the valve Cis opened for providing communication between the raw air and waste gaspaths so as to equalize the pressurethereof, considerable amounts of rawair and waste gas are mixed in the block so that when the valve C, isopened, a considerable amount of raw air is discharged together with thewaste gas, the result being that the loss of the raw air becomessignificant. Also, since the pressure of thewaste gas paths variesabruptly, a large noise is generated, so that a silencer is required. Inaddition, this abrupt pressure change breaks the gas-liquid equilibriumin the rectification process thus disturbing and making it difficult tomaintain a stable rectification.

Further, as shown in FIG. 2, in an arrangement having a cooling tower 70and an evaporative cooling tower 71, raw air supplied from a pipe 72 iscooled at the cooling tower 70 with water and the water is cooled bywaste gas, or waste nitrogen, at the evaporative cooling tower 71, andwaste gas is accordingly fed to the'evaporative cooling tower 71.However, when raw air of approximately 5 atm. and waste gas ofapproximately 0.2 atm. are exchanged, the aforementioned abrupt pressurechange occurs, and if the pressure change is effected directly at theevaporative cooling tower 71, the filler within the evaporative coolingtower may be ejected from the tower or be broken with the result that athree-way change-over valve 73 must be provided to avoid the effects ofthe pressure change by discharging the waste gas through a pipe 74 uponthe exchange thereof.

SUMMARY OF THE INVENTION This invention contemplates the elimination ofthe aforementioned various disadvantages of presently available devicesand the provision of a novel and improved reversing heat exchanger unitin which the re- BRIEF DESCRIPTION OF THE DRAWINGS Other objects,features and attendant advantages of the present invention will be morefully appreciated as the same becomes better understood from thefollowing detailed description when considered in connection with theaccompanying drawings, in which like reference numerals designate likeor corresponding parts throughout the several views, and wherein:

FIG. 1 is a diagrammatic view of a conventional reversing heat exchangersystem in an air separator;

FIG. 2 is a diagrammatic view of another conventional reversing heatexchanger system;

FIG. 3 is a side sectional view of one embodiment of a change-over valveconstructed according to the present invention;

FIG. 4 is a side sectional view of one embodiment of a check valveconstructed in accordance with the present invention;

FIG. 5 is a schematic illustration of another embodiment of a checkvalve constructed according to the present invention;

FIG. 6 is a schematic illustration of a reversing heat exchanger unithaving the change-over valves and check valves of this invention;

FIG. 7 is an explanatory illustration of another reversing heatexchanger unit having the change-over valves shown in FIG. 3 and thecheck valves shown in FIG. 1;

FIG. 8 is an explanatory illustration of a further reversing heatexchanger unit having a change-over valve according to this inventionprovided with flow rate control valves;

FIG. 9 is an explanatory illustration of a reversing heat exchanger unitsuch as shown in FIG. 8 having an integral flow rate control valveincorporated therein; and

FIG. 10 is a diagrammatic view of an embodiment of a reversing heatexchanger system having six heat exchanger units constructed accordingto the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS Reference is nowmade to the drawings, particularly to FIG. 3, which shows one embodimentof a changeover valve constructed according to the present invention andcomprising a pair of opposing valve bodies 41 and 42 positioned on avalve rod 43 to form three chambers M,, M, and M partitioned within thehousing thereof having a nozzle 52 disposed in the central chamber M andtwo nozzles disposed in each of the outer chambers at both ends thereof,namely nozzles 48 and 50 in chamber M, and nozzles 49 and 51 in chamberM wherein the materials flowing in the path formed by the two nozzles inone of the outside chambers and a path formed by one nozzle in the otheroutside chamber and the nozzle in the central chamber may be readilyexchanged by movement of the valve rod. Thus, the valve bodies 41 and 42provide contacting surfaces 41a, 41b and 42a, 42b on the opposingsurfaces thereof, respectively, so that the valve bodies 41 and 42cooperate with the back and forth, oraxial, movement of the valve rod 43by an operating piston 44 to open the central chamber M and its nozzle52 to one of the nozzles of one of the outside chambers, while closingthe other nozzle of the one outside chamber and also permitting flowthrough the other outside chamber from its one nozzle to the other. Thenozzles 50 and 51 provided at the tops of the outside chamber M and M;,,respectively, are nozzles communicating with the heat exchanger, thusproviding an outlet of raw air and an inlet of waste gas, while thenozzles 48 and 49 respectively provided in the bottoms of the outsidechambers M and M are inlet nozzles for raw air and the nozzle 52provided in the central chamber M is an outlet nozzle for waste gas.

The contacting surfaces 41a and 42a of the valve bodies 41 and 42 facethe raw air inlets of the nozzles 48 and 49, respectively, and thecontacting surfaces 41b and 42b face the waste gas outlet of the nozzle52 in their disposition in the valve housing forming the respectiveinlets and outlets. The operating piston 44 of the valve rod 43 isdisposed within a cylinder having an inlet 46 and an outlet 47 foroperating air, and a cushion 45 is provided at the other end of thevalve rod 43 to be disposed within a cylinder therefor, but themechanism for moving the valve rod 43 and the cushion mechanismobviously may take other forms capable of functioning the same.

In operation of the change-over valve, if operating air is fed into thecylinder from an inlet 46 so as to push the operating piston 44leftwardly of the drawing, as shown in FIG. 3, the contacting surfaces41a and 42b of the valve bodies 41 and 42 will close the path of thenozzle 48 and one of the paths of nozzle 52, respectively, so that rawair flows from the nozzle 49 to the nozzle 51 and waste gas flows fromthe nozzle 50 to the nozzle 52. Then, if operating air is reversely fedfrom outlet 47 into the cylinder end is exhausted from the inlet 46, theoperating piston 44 moves rightwardly as viewed in the drawing so thatthe contacting surfaces 41b and42a of the valve bodies 41 and 42 closethe path of nozzle 49 and another of the paths of nozzle 52,respectively, with the result that the contacting surfaces 41a and 42bare separated from their seats. As a result, raw air flows from thenozzle 48 to the nozzle 50 and waste gas flows from the nozzle 51 to thenozzle 52 by one simple operation to complete the exchange thereof.

In this change-over valve, the surfaces of the valve bodies 41 and 42facing the chambers M and M always receive the pressure of raw air.Thus, if the surface contacting the outlet of thenozzle 48 of thechamber M is closed as shown in FIG. 3, the valve body 42 receives theforce of 11' PDI4 from the surface thereof on the chamber M side beingapplied leftwardly of the drawing, while the valve body 41 receives theforce of 1r Pd /4 from the surface of the nozzle 48 side being appliedrightwardly of the drawing, where D illustrates the diameter ofcontacting surfaces 41b and 42b of the chamber M side, d the diameter ofthe contacting surfaces 4la and 42 1v of the raw air side, and P thepressure of the raw air. Consequently, the valve rod 43 receives theforce of P(D J )/4 being applied leftwardly of the drawing. In order tomove the rod 43, if raw air of pressure P is used as operating air ofthe operating piston 44 to be supplied from the inlet-outlet arrangement46 and 47, the diameter of the o erating piston 44 may be slightlylarger than E with the result that the cylinder containing the operatingpiston 44 may accordingly be kept small. In such case, though the sizesof the contacting surfaces 41a, 41b and 42a, 42b may be equalized, itthen is necessary to enlarge the operating piston so as to obtain thesurface pressure at the contacting surface required for their sealing,whereas the operating piston may be lessened if the contacting surfaces41b and 42b are larger than the contacting surfaces 41a and 42a so as toobtain the surface pressure required for their sealing due to their areadifference, as shown in FIG. 3.

It is advantageous since the raw air is compressed air of approximately5 atm., the raw air may be used for the operating air of the operatingpiston 44.

Although the check valve used in this invention may be a pair of checkvalves heretofore known, as shown in FIG. ll, the check valve shown inFIG. 4, which shows one embodiment of a check valve constructedaccording to the present invention, is preferably employed.

This check valve comprises a body 20 divided into three adjacentchambers, including a central chamber R and two outside chambers R, andR by two partition walls 23 and two outer walls 29, the chambersrespectively having normally open ports, and four valve bodies movableby pressure differences occurring between adjacent chambers and beingmounted symmetrically at the center of the central chamber with two ofthe valve bodies disposed in the partition walls and the other valvebodies being disposed on the outer walls of the two outside chambers.More particularly, the three chambers R,, R, and R are partitioned byvalve bodies l4, l5, l6 and 17 mounted on partition walls 23 and outerwalls 29, and piping nozzles 30 through 34 are provided in each chamber.In this embodiment, the valve bodies 14, 17 and 15, 16 are oppositelymounted outwardly with respect to the central chamber R and areconnected to the partition walls 23 and outer walls 29 by valve bases 24fixed thereto at one end thereof through sealing plates 25 fixed to oneend of a movable arm 26 through a connecting pin 18, the sealing plate25 contacting an area with the valve base 24 for sealing gas flow by theback pressure so as to open the valve body if the pressure on thesurface 27 is larger than the back pressure.

In operation of thecheck valve constructed in this manner, raw air ofapproximately 5 atmospheres being supplied from the heat exchanger isfedinto one chamber R, of the check valve through the piping nozzle 32so as to seal the valve body 14. with a pressure of approximately 5 atm.and to open the valve body 15 with the same pressure, and is fed throughthe chamber R, from the piping nozzle 34 into a rectification system. Onthe other hand, waste gas of approximately 0.2 atmospheres fed from therectification process opens the valve body 17 being introduced from thenozzle 31 into chamber R, of the check valve to be fed therefrom throughthe nozzle 33 to the heat exchanger.

In this case, since the valve body 16 receives pressure of approximately0.2 atm. from the waste gas upon the front surface, but also receives aback pressure of approximately 5 atm. from the chamber R, side, it re- Irespect to the central chamber R which case is shown in FIG. 5.

The check valve of the embodiment shown in FIG. 5 comprises threechambers R,', R and R partitioned by partition walls 23, outer walls 29and valve bodies 14, 15, 16 and 17, and spaces S, and S, are provided inthe range of the movable valve bodies 14 and 17 at the mounting portionsof the nozzles 30 and 31.

In operation of a check valve so constructed, raw air of approximately 5atm. supplied from the heat exchanger is fed through the nozzle 32 intothe chamber R, to open the valve body 14 and is supplied through thenozzle 30 into the rectification system, not shown. On the other hand,waste gas of 0.2 atm. supplied from the rectification system is fedthrough the nozzle 34 into the central chamber R to open the valve body16 and is supplied from the nozzle 33 into the heat exchanger. Here,since the valve body receives a front surface pressure of approximately0.2 atm. from the chamber R side, but also receives a back pressure ofapproximately 5 atm. from the chamber R, side, it is closed, and sincethe valve body 17 similarly receives a front surface pressure ofapproximately 0.2 atm. from the chamber R side but also receives thepressure of raw air, i.e., a back pressure of approximately 5 atm. fromthe space S, communicating with the nozzle 31, it remains closed. Then,if the paths of the heat exchanger are exchanged, the valve bodies 14through 17 are opened or closed in an opposite fashion so that raw airis supplied through the heat exchanger, nozzle 33, chamber R and nozzle31 into the rectification system, while waste gas is fed through thenozzle 34, chambers R and R,', and nozzle 32 into the heat exchanger.

Referring now to FIG. 6, there is shown a reversing heat exchanger unithaving a change-over valve and check valve wherein the check valve B isprovided at the low-temperature side of the reversing heat exchanger Awhile change-over valve C is provided at the high temperature sidethereof.

In operation of this reversing heat exchanger unit, in

case of an all low-pressure type air separator, raw air of approximately5 atm. is fed from the nozzle 48 of the change-over valve C through thenozzle 50 as designated by an arrow in FIG. 6, then into the heatexchanger body so as to exchange heat with the counter current waste gasfor being cooled to approximately C. and is then fed from the nozzle 32into the chamber R, of the check valve B to seal the valve body 14 by apressure of approximately 5 atm. and to open the valve body 15 by thesame pressure and whereafter itis supplied from the chamber R throughthe nozzle 34 to the rectification system or the lower portion of arectification tower, not shown. 0n the other hand, waste gas ofapproximately 0.2 atm. from the upper portion of the rectification toweropens the valve body 17 to be introduced into the. chamber R of thecheck valve B from the nozzle 31 then through the nozzle 33 to heatexchanger A to become substantially normal in temperature, and is thenfed through the nozzle 31 into the change-over valve C so as to be fedfrom the nozzle 52 into the pipe for feeding out the waste gas. If theraw air and waste gas paths in the heat exchanger are exchanged,operating air is fed into the piston chamber of the change-over valve Cfrom the inlet 46 and operating air from the outlet 47 is exhausted, sothat the operating piston 44 moves leftwardly of the drawing with theresult that the contacting surfaces 41a and 42b of the valve bodies 41and 42 close the communicating portions between the nozzles 48 and 50and 51 and 52 and the contacting surfaces 41b and 42a are separated fromtheir seats. Consequently, raw air is fed from the nozzle 49 and throughnozzle 51, while waste gas is fed from the nozzle 50 and through thenozzle 52, the exchange being effected by one simple operation. Sincethe pressures before and after the valve bodies 14 through 17 of thecheck valve are varied by the exchanging operation of the change-overvalve C, the valve bodies 14 and 16 are opened, while the valve bodiesand 17 are closed, to complete the exchange operation, and raw air issupplied from the nozzle 33 through the chambers R and R and the nozzle34, then into the rectification process, while waste gas is suppliedfrom the nozzle through the chamber R, and the nozzle 32, then into theheat exchanger.

In FIG. 6, since the product gas paths of the reversing heat exchangerhave no relation to the exchange thereof, they are omitted. And, sincethe product gas paths are not related even in the following aspects,they will be omitted hereinafter also.

Reference is now made to FIG. 7, which shows the reversing heatexchanger unit having the change-over valve shown in FIG. 3 and thecheck valves known heretofore, as shown in FIG. 1.

The upper nozzles 50 and 51 provided in the outside chambers M, and M,of the change-over valve C are connected to the high temperature side ofthe heat exchanger A, while a pair of check valves B, and B areconnected to the low temperature side thereof, so that these areunified.

In operation of the reversing heat exchanger unit so constructed, rawair is fed through the nozzles 48 and 50 of the change-over valve C intothe heat exchanger A and then through the check valve B, into therectification system, while waste gas is-fed through the other checkvalve B, into the heat exchanger A and further through the nozzle 51 ofthe check valve C and the central chamber M to the nozzle 51 and theninto the pipe for feeding out waste gas. The exchange of the raw air andwaste gas paths of the heat exchanger is as previously described.

Referring now to FIG. 8, there is shown a further embodiment of thereversing heat exchanger unit illus-' trated in FIG. 6, having flowcontrol valves D,, D," and D provided in the nozzles 48, 49 and 52,respectively, of the change-over valve C.

As seen from the description of the reversing heat exchanger unit shownin FIG. 6, in the operation of this heat exchanger unit, since .wastegas flows through the nozzle 52 of the change-over valve C regardless oftheir exchange while only raw air passes through the nozzles 48 and 49,the flow rate control valves D, and D," always adapt for raw air flow soas to adjust the valve opening, while the flow rate control valve Dalways adapts for waste gas flow so as to adjust the valve opening. Ifthe change-over valve is operated after these flow rate control valvesD,', D," and D are closed, the pressure of raw air and waste gas pathsmay be equalized.

Reference is now made to FIG. 9, which shows still another embodimentofa reversing heat exchanger unit having an integral flow rate controlvalve unifying the flow rate control valves D, and D," of raw air into asingle unit and wherein the other components are the same as those inthe unit shown in FIG. 8. The reversing heat exchanger unit shown inFIG. 7 may also be supplied with the flow rate control valves used inthe units shown in FIGS. 8 and 9, without other modification, ifdesired.

Referring now to FIG. 10, another embodiment of a reversing heatexchanger system using six heat exchanger units constructed according tothe present invention, as shown in FIG. 8, is illustrated. In operation,raw air supplied from the main pipe 60 is supplied through change-overvalves C, through C, to heat exchanger units A, ,through A,,, thenthrough check valves B, through E, to be gathered in the main pipe 63for passage to a rectification process, while waste gas is gathered fromthe main pipe 62 through check valves B, through B heat exchangers A,through A,,, and change-over valves C, through C being collected in themain pipe 61 to be fed out of the exchanger. Here, flow rate controlvalves D,, D, and D correspond to the flow rate control valves D, and Dshown in FIG. 1 for controlling the flow rate of raw air and waste gaspassing through the heat exchanger. In FIG. 1, since raw air and wastegas flow alternatively through the flow control valves D, and D, inevery exchange of flow paths, its control was difficult, but if theinstant reversing heat exchanger unit is adopted, raw air always flowsthrough the flow rate control valves D, and D,", while waste gas flowsalways through the flow rate control valve D and accordingly it is veryeasy to control the flow rate thereof. And, since the flow rate controlvalves D, and D, are closed upon exchange, the pressure of raw air andwaste gas may be equalized upon exchange.

It should be understood from the foregoing description that thefollowing effects and advantages are provided by improving theconventional art in a manner suggested by this invention.

a. Since the respective reversing heat exchanger units are not formed inblocks but are unified, it may be freely exchanged in response to therespective types of the exchanger.

b. Since the design condition of the capacity of the air separationplant depends only upon the number of the reversing heat exchangerunits, a plan or schedule may be quickly and accurately conducted.

c. Since the treating capacity of the unit is constant, the capacity ofthe change-over valve and check valves become constant accordingly sothat they may be unified to provide a mass production and thus toimprove the quality of the product and to cut costs.

Since the change-over valves and check valves are directly mounted to beunified in the respective reversing heat exchanger unit, the main pipes10 and 11 between the check valves and the heat exchanger and the mainpipes 12 and 13 between the heat exchanger and the change-over valve areunnecessary, the exchange capacity or volume between raw air and wastegas becomes minimum so that the exchange loss of raw air is reduced 25to 40 percent in comparison with the conventional types, and further,exchange noise may be lessened to an extent impossible in theconventional exchanger without use of a silencer. e. Though the pressuredue to the closing are of the change-over valves upon exchange breaksthe gasliquid equilibrium in the conventional reversing heat exchangerhaving blocks of heat exchangers, the respective unit may beindependently exchanged in the device of this invention, and accordinglytentative pressure increase thereof is sufficiently absorbed by the mainpipes 62 and 63 shown in FIG. to have no affect on the rectificationsystem and thus to provide a stable rectification.

If the unit of this invention is adopted, the height of the cold box ofthe heat exchanger of the air separator may be lowered so as to decreasethe volume of the box 20 to 30 percent in comparison with conventionalexchangers.

g. If one block of reversing heat exchanger units is exchanged by 4 or 5change-over valves as heretofore practiced, it is necessary to exchangethe respective valves in cooperation with each other, and accordingly ifany one becomes defective in operation, raw air and waste gas are mixedto badly affect the air separator, but in the unit of this invention,the exchange period of the unit provided with the change-over valve ismerely lengthened, and even if the change-over valve becomes defectivein operation it will not affect the separator, whereby the stability ofthe separator is improved.

h. Since the fluids passing through the respective flow rate controlvalves are not related to the exchange of the flow paths but are alwaysthe same through the provision of the flow rate control valves D,', D,"and D shown in FIG. 8, and valves D and D shown in FIG. 9 in the pathsof the nozzles 48, 49 and 52 of the change-over valves, it is extremelysimple and easy to control the flow rate of the fluid.

1'. Raw air and waste gas paths in the reversing heat exchanger unit maybe readily equalized in pressure merely by closing fully the flow ratecontrol valves shown in FIGS. 8 and 9.

Obviously many modifications and variations of the invention arepossible in light of the above teachings. Accordingly, it is thereforeto be understood that within the scope of the appended claims thisinvention may be practiced otherwise than as specifically describedherein.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

l. A reversing heat exchanger unit for performing a heat exchangeoperation between two gases, comprising:

a reversing heat exchanger;

a change-over valve connected to temperature side of said reversing heatexchanger;

a check valve connected to the low-temperature side of said reversingheat exchanger; and

flow rate control valves connected tosaid changeover valve,

the high.

wherein the change-over valve is a housing divided into two sidechambers and a central chamber with a nozzle, the side chambers eachhaving two other nozzles with one of the nozzles of each side chamberbeing connected to the high-temperature side of the heat exchanger, aflow path for one of said gases being formed by each of the nozzlesconnected to the high-temperature side of the heat exchanger and thenozzle in the central chamber, an alternate flow path for the other oneof said gases being formed by each of the nozzles connected to thehigh-temperature side of the heat exchanger .and the other nozzles inthe respective side chamber, and valve means in said housing forexchanging the paths being formed therein between the nozzles, andwherein further, said flow rate control valves are connected to saidother nozzles of said side chambers and said nozzle of said centralchamber.

2. A reversing heat exchanger unit according to the claim 1, whereinsaid check valve is a housing having three chambers formed by a pair ofspaced partition walls and opposite outer walls of said housing, each ofsaid three chambers having a normally open port and four valve bodiespositioned one each in each of said walls being movable by pressuredifference between adjacent chambers and mounted symmetrically from thecenter of the central chamber.

3. A reversing heat exchanger unit according to claim 1 wherein saidvalve means in said housing of said change-over valve comprises:

a pair of valve bodies mounted on a valve rod axially movable withinsaid housilig;

each of said pair of valve bodies having opposing contacting surfacesfor alternately opening and closing a different one of said paths formedby said nozzles connected to the high temperature side of said reversingheat exchanger and the nozzle of said central chamber and the pathsformed by the same said nozzles connected to the hightemperature side ofsaid heat exchanger and said other nozzles in the same chambers uponmovement of said valve rod.

4. A reversing heat exchanger unit according to claim 3, furthercomprising a cylinder and a fluid pressureoperated piston connected toone end of said valve rod and slidable within saidcylinder for movingsaid valve rod.

5. A reversing heat exchanger unit according to claim 1 wherein saidflow rate control valves are respectively provided in a gathering pipecommunicating with said other nozzles of said side chambers notconnected to the high-temperature side of said heat exchanger and in thenozzle in said central chamber.

1. A reversing heat exchanger unit for performing a heat exchangeoperation between two gases, comprising: a reversing heat exchanger; achange-over valve connected to the high-temperature side of saidreversing heat exchanger; a check valve connected to the low-temperatureside of said reversing heat exchanger; and flow rate control valvesconnected to said change-over valve, wherein the change-over valve is ahousing divided into two side chambers and a central chamber with anozzle, the side chambers each having two other nozzles with one of thenozzles of each side chamber being connected to the high-temperatureside of the heat exchanger, a flow path for one of said gases beingformed by each of the nozzles connected to the high-temperature side ofthe heat exchanger and the nozzle in the central chamber, an alternateflow path for the other one of said gases being formed by each of thenozzles connected to the hightemperature side of the heat exchanger andthe other nozzles in the respective side chamber, and valve means insaid housing for exchanging the paths being formed therein between thenozzles, and wherein further, said flow rate control valves areconnected to said other nozzles of said side chambers and said nozzle ofsaid central chamber.
 2. A reversing heat exchanger unit according tothe claim 1, wherein said check valve is a housing having three chambersformed by a pair of spaced partition walls and opposite outer walls ofsaid housing, each of said three chambers having a normally open portand four valve bodies positioned one each in each of said walls beingmovable by pressure difference between adjacent chambers and mountedsymmetrically from the center of the central chamber.
 3. A reversingheat exchanger unit according to claim 1 wherein said valve means insaid housing of said change-over valve comprises: a pair of valve bodiesmounted on a valve rod axially movable within said housing; each of saidpair of valve bodies having opposing contacting surfaces for alternatelyopening and closing a different one of said paths formed by said nozzlesconnected to the high temperature side of said reversing heat exchangerand the nozzle of said central chamber and the paths formed by the samesaid nozzles connected to the high-temperature side of said heatexchanger and said other nozzles in the same chambers upon movement ofsaid valve rod.
 4. A reversing heat exchanger unit according to claim 3,further comprising a cylinder and a fluid pressure-operated pistonconnected to one end of said valve rod and slidable within said cylinderfor moving said valve rod.
 5. A reversing heat exchanger unit accordingto claim 1 wherein said flow rate control valves are respectivelyprovided in a gathering pipe communicating with said other nozzles ofsaid side chambers not connected to the high-temperature side of saidheat exchanger and in the nozzle in said central chamber.